| Hmm, well, better, but still... | So, after some more tracing and fiddling with m4, I think the definition | of m4_foreach in m4sugar.m4 is highly non-optimal. Currently it is: | | m4_define([m4_car], [$1]) | m4_define([_m4_foreach], | [m4_if(m4_quote($2), [], [], | [m4_define([$1], [m4_car($2)])$3[]_m4_foreach([$1], | [m4_shift($2)], | [$3])])]) | | A trace reveals, that the quoting of the m4_shift call makes all the | m4_shift's add up. They get only evaluated for the m4_quote() and the | m4_car() calls in the next iteration.
Yes, it is precisely to protect the items and to preserve quotation. I didn't find any means to preserve the quotation and to be eager. | This adds up like so: (quoting is wrong) | | m4_fe (f, (a,b,c), bla) | quote(a,b,c) -> [a,b,c] != "" | car(a,c,b) -> a | m4_fe (f, shift(a,b,c), bla) | quote(shift(a,b,c)) -> quote(b,c) -> b,c != "" | car(shift(a,b,c)) -> car(b,c) -> b | m4_fe (f, shift(shift(a,b,c)), bla) | quote(shift(shift(a,b,c))) -> quote(shift(b,c)) -> quote(c) -> c != "" | car(shift(shift(a,b,c))) -> car(shift(b,c)) -> car(c) -> c | | Now guess what happens with 334 listitems. shift's of the same argument | lists are evaluated again and again (i.e. quadratic behaviour). Right :( I didn't think that m4_foreach could be _the_ responsible :( | Forthermore I believe the definition of m4_car is wrong. If I test | m4_foreach with the example in the explanation in m4sugar.m4... : | | m4_define(a, 1)dnl | m4_define(b, 2)dnl | m4_define(c, 3)dnl | m4_foreach([f], m4_split([a (b c)]), [echo f | ])dnl | | ... the output is: | echo 1 | echo (2 | echo 3) Because split has changed too. | If I define m4_car like so: | m4_define([m4_car], [[$1]]) | it becomes | echo a | echo (b | echo c) | | So, for now I work with that definition of mm_foreach and AC_FOREACH: | | m4_define([mm_foreach], | [m4_pushdef([$1])_mm_foreach($@)m4_popdef([$1])]) | m4_define([mm_car], [[$1]]) | m4_define([mm_car2], [[$@]]) | m4_define([_mm_foreach], | [m4_if(m4_quote($2), [], [], | [m4_define([$1], [mm_car($2)])$3[]_mm_foreach([$1], | mm_car2(m4_shift($2)), | [$3])])]) | m4_define([AC_FOREACH], | [mm_foreach([$1], m4_split(m4_normalize([$2])), [$3])]) I am now more convinced than I was before that m4_foreach and friends are wrong, we really ought to work with recursion instead of pseudo for loops. | Note how mm_car2 is used for evaluating the m4_shift($2), but how it still | quotes it's own arguments. The above mm_foreach produces the correct | output for the example above, and also, when inserted into configure.in | the same configure file. I again use the autoconf version of | AC_CONFIG_FILES (i.e. without removing the .._UNIQUE and | ..._DEPENDENCIES), and the only difference now is this: | | # time autoconf-2.5x | real 0m18.634s | | Much better. | | Any comments? Yep, this is really impressive, congrats! I have one question though: did you run the test suite? How does your proposal behave?
